Soft bond for semiconductor dies

ABSTRACT

On a semiconductor integrated circuit die, a semipermanent electrical connection is effected by the use of wirebond techniques, in which the parameters of the wirebond are controlled, so that less bonding force retains the leadwires to the bondpads than the attachment strength of the bondpads to the die. The wirebond techniques include attaching leadwires to bondpads on the die, using ultrasonic wedge bonding. The strength of the bond between the leadwires is significantly less than the attachment strength of the bondpads, preferably by a ratio which ensures that the bondpads are not lifted from the die when the leadwires are removed by breaking the bond between the leadwires and the bondpads. Subsequent to testing and burnin, the bond between the leadwires and the bondpads is severed. The die are then removed from the package body and the bondpads may then be attached by conventional means. The technique is useful in providing known good die.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation-in-part application to U.S. Pat. No. 5,173,451,filed as U.S. patent application Ser. No. 889,008, on May 26, 1992. U.S.Pat. No. 5,173,451 is a continuation-in-part to U.S. patent applicationSer. No. 07/788,085, filed Nov. 5, 1991, which is a continuation-in-partto U.S. patent application Ser. No. 07/709,858, filed Jun. 4, 1991.

FIELD OF THE INVENTION

This invention relates to the establishment of connections for testingof the response of digital electronic devices in order to properlydetermine the functionality of integrated circuits. More particularly,it relates to electrical connections of semiconductor integrated circuitdies to leadframes and the like on a temporary basis in order to performtesting and burnin of the integrated circuit dies.

BACKGROUND OF THE INVENTION

Integrated circuit memory devices, such as dynamic random accessmemories (DRAMs) and static random access memories (SRAMs) undergotesting by the manufacturer during production and often by the end user,for example, in a memory test conducted during computer initialization.As densities of the memory device increase, so that individual IC's arecapable of storing sixteen or more megabits of information, the timenecessary for testing the IC's increases as well.

In addition, there is an increased interest in providing parts which arefully characterized prior to packaging. This is desired not only becauseof the cost of the package, but also because there is demand formulti-chip modules (MCMs), in which multiple parts in die form aretested and assembled into a single unit. While there are varioustechniques purposed for testing, burning in and characterizing asingulated die, it would be advantageous to be able to "wafer map" thedie prior to assembly with as many performance characteristics aspossible. Ideally, one would want to be able to map the wafer with fulldevice characterization.

MCMs create a particular need for testing prior to assembly, ascontrasted to the economics of testing parts which are discretelypackaged as singulated parts. For discretely packaged parts, if theproduct yield of good parts from preliminary testing to final shipment(probe-to-ship) is, for example, 95%, one would not be particularlyconcerned with packaging costs for the failed parts, if packaging costsare 10% of the product manufacturing costs. Even where packaging costsare considerably higher, as in ceramic encapsulated parts, testingunpackaged die is economical for discretely packaged parts when theadded costs approximates that of cost of packaging divided by yield:##EQU1## where

C=cost

C_(DIE) =manufacturing cost of functional die

C_(ADDL).KGD =additional cost of testing unpackaged die in order toproduce known good die (KGD)

Note that in the case of discretely packaged parts, the cost of the die(C_(DIE)) is essentially not a factor. This changes in the case of MCMs:##EQU2## Note that again C_(DIE) is not a factor in modules havingidentical part types; however, the equation must be modified to accountfor varied costs and yields of die in modules with mixed part types.

With MCMs, the cost of packaging a failed part is proportional to thenumber of die in the module. In the case of a ×16 memory array module,where probe-to-ship yield of the die is 95%, the costs are: ##EQU3## sothe additional costs of testing for known good die (KGD) may be 16 timesthe cost of testing after assembly of an unrepairable module in order tobe economical. This, of course, is modified by the ability to repairsome failed modules.

One of the test procedures which is used to determine the viability ofsemiconductor integrated circuits is burnin. In the burnin procedure,the parts are exercised for a period of time with different temperaturecycles, including at elevated temperatures. This procedure provides anindication of the operation of the device at the different operatingtemperatures, and also results in a determination of early partfailures. During the burnin process, such early failures, known as"infant mortality," is predicted to occur within a particular amount oftime. Therefore, if it can be determined that almost all such failuresoccur within the first 48 hours of burnin testing, then the burnin testcan be completed within that time period. Such factors as temperature,process and device type influence when failures stop happening, so thespecific burnin time period will vary with part type and other factors.In the case of testing of packaged discrete devices, each device is ableto be separately monitored by external test equipment, so that theexternal test equipment can be used to provide an indication of the timeof failure of that particular part.

In testing die prior to encapsulation, temporary electrical connectionmust be effected between the die and a fixture. This is accomplished inthe bond region, either at the bondpads or closely adjacent the bondpad.In the case of wirebond die, the bondpads is often produced at a levelwhich is not raised above the top surface of the die and may be recessedbelow the top surface.

One process which causes the top of the bondpads to be recessed is onein which the bondpads are formed, but not formed with raised topography,followed by the formation of a passivation layer. The bondpads are leftexposed through the passivation layer, but are recessed below the top ofthe passivation layer. During wirebonding, the recessed position of thebondpads is inconsequential, but this can create a problem with otherattachment techniques. If the die are to be tested prior toencapsulation, the die must be compatible with both the test attachmentand the later permanent attachment, and the test attachment must notdamage the die in such a way as to inhibit permanent attachment.

In a prior art technique, raised conductive portions of conductivelayers could be formed by photoplating. The raised portion is a bumpwhich is used as an electrical contact so that, when a plate is broughtinto contact with a semiconductor die, the bump engages a bondpad on thedie. This contact of the bump with the bondpad on the die presents twoproblems; dimensional accuracy and distortion.

The raised portions engage diebond pads on the die and the raisedportion is compressed against the diebond pads. Subsequent to the raisedportion being used, it may be desired to separate the conductive layer,and thereby disconnect the connector from the diebond pads on the die.At this point, the raised portions have been compressed and areunsuitable for reuse without being reformed.

When the bump is used as an electrical contact to engage a bondpad on asemiconductor die, dimensional accuracy is a requisite. Bondpads onsemiconductors are made small (approximately 100μ) in order to conserveuseful surface area, known as "real estate," on the die. In the case ofwirebonded die, the size of the bondpad is usually selected to besufficient to permit a wirebonder to reliably establish wirebondconnections to the die. Other connection techniques, such as TAB, havetheir own requirements, but the bondpads are similarly restricted insize.

The bondpads used in wirebonded die are usually recessed below apassivation layer. The passivation layer is a film of insulator, such asBPSG, and can form a barrier to effective contact of the bump with thebondpad if the bump is too large or is out of alignment.

Other techniques include ball bonding, in which wirebonding techniquesare used to deposit a small amount of material on a conductive portion.Rather than permitting a wire to remain attached to the bondsite,sufficient energy is applied to the wirebonder to cause the wire tobreak from the bondsite, thereby leaving an attached portion of thewire, known as a ball bond. The material for this process must of coursebe selected in order to permit the process to be properly implemented.

In a prior art technique, raised conductive portions of conductivelayers could be formed by a process known as doinking. In doinking, araised portion of conductive material is formed from material bybringing a probe in close proximity to the material and applying energyto the material. In the preferred embodiment, the probe has a centeropening and the applied energy is a combination of thermal energy andultrasonic mechanical vibration of the probe. The process, known asdoinking, uses ultrasonic forging and results in a doink, which consistsof a raised portion of the material, surrounded by a crater.

SUMMARY OF THE INVENTION

According to the invention, a semipermanent electrical connection iseffected by the use of wirebond techniques, in which the parameters ofthe wirebond are controlled sufficiently to permit the semipermanentconnection to be removed without significantly damaging the die.

This is accomplished by first preparing a semiconductor integratedcircuit die, including bondpads such as wirebond pads or bondpads forTAB (tape automated bonding) electrical connections.

A precured RTV silicone strip, commonly known as "gel pack," is used fortemporarily securing the die in place within a package body. The backingstrip exhibits a surface static charge sufficient and coefficient offriction sufficient to hold the die in place without adhesive.

Leadwires are attached to the bondpads, preferably by the use ofultrasonic wedge bonding, with less bonding force retaining theleadwires to the bondpads than the attachment strength of the bondpadsto the die. Subsequent to testing and burnin, the bond between theleadwires and the bondpads is severed. The strength of the bond betweenthe leadwires is significantly less than the attachment strength of thebondpads, preferably by a ratio which ensures that the bondpads are notlifted from the die when the leadwires are removed by breaking the bondbetween the leadwires and the bondpads. The die are then removed fromthe package body and the bondpads may then be attached by conventionalmeans, such as wirebonding, TAB or flip chip bonding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a top view of substrate on which a softbond wirebondconnection has been established by the inventive techniques;

FIG. 2 shows a cross-section of the substrate of FIG. 1;

FIG. 3 shows the cross-section of FIG. 1 subsequent to removal of thewirebond connection;

FIG. 4 is a low resolution scanned photomicrograph, showing a wirebondconnection formed in accordance with the preferred embodiment; and

FIG. 5 is a low resolution scanned photomicrograph, showing a bondpadsubsequent to severing the wirebond connection of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 and 2, the inventive burn-in fixture 11 includes apackage body, 13 and a cover plate 15. The package body 13 includes adie receiving cavity 17.

The die receiving cavity 17 has dimensions which are at least sufficientto accommodate a die 21. The die 21 is to be connected at bondpads 27,which are typically 0.1 mm wide. The package body 13 therefore functionsas a die carrier for the purpose of such things as burnin and testing ofthe die 21.

The package body 13 is preferrably provided with a hole or slot 31 whichpermits convenient access to the bottom of the die 21 in order that thedie 21 may be lifted out of the die receiving cavity 17. In thepreferred embodiment, a round hole is used, since it is easier tofabricate.

It is possible to provide a package body without a hole. If the hole isnot provided, removal of the die 21 from the die receiving cavity 17 isaccomplished by using tweezers to lift the die 21 from the package body13. If adhesive is used to secure the die 21 in the die receiving cavity17, then heat may be applied to the package body 13 to facilitateremoval of the die 21.

A plurality of external connector leads 33 extend from the burn infixture 11. These external leads 33 are used to connect the die 21 toexternal test and burnin circuitry, in the manner of the leads of anintegrated circuit part. These leads may take the form of leadwires orribbons.

As can be seen in FIG. 2, in the preferred embodiment, the externalconnector leads 33 are attached to the package body 13, and extendtherefrom. The external connector leads 33 are shown as connector pins,which preferably are in a DIP (dual inline package) or QFP (quad flatpack) configuration.

The external connector leads 33 are secured by the package body 13 andterminate on the package body 13 with contact pads 37. The contact pads37 are in approximate planar alignment with the bondpads 27. Thebondpads 27 are typically recessed below a top surface level 43,established by a BPSG passivation layer 45.

Referring to FIGS. 1 and 2, connections between the contact pads 37 onthe package body 13 and the bondpads 27 are effected by leadwires 51.The leadwires 51 therefore are able to conduct signals between thebondpads 27 and the contact pads 37, so that an electrical connection isestablished between the bondpads 27 and contact pads 37.

It is believed that an optimum technique for temporarily securing thedie 21 in place in the package body 13 is a material which exhibits astatic charge sufficient to hold the die 21 in place within the packagebody 13 during the attachment of the leadwires 51 to the bondpads on thedie 21. The static charge results in a charged surface state whichattracts the die 21 to the material. One material which exhibits asufficient static charge is a silicone based polymer. In one preferredembodiment, we use a precured RTV silicone strip, commonly known as "gelpack," as a backing strip 55. The backing strip 55 exhibits a staticcharge sufficient and coefficient of friction sufficient to hold the die21 in place without adhesive, and also is elastomeric. In other words,the silicone holds the silicon in place.

Another preferred embodiment which uses a material which exhibits asufficient static charge includes the application of a liquid. Thisliquid preferrably cures in place as a silicone based polymer. The curedliquid exhibiting a static charge sufficient to hold the die in place.

An alternative technique, which has been tested in prototype testprocedures using this invention, utilizes a tape type die attachadhesive, sold by E.I. dupont de Nemours of Wilmington, Del., under thetrademark Kapton QL Die Attach Adhesive. The QL adhesive is heated, butfor a shorter time period than for permanently packaged die. This allowsa standard process setup to be used for temporary die attach, whilepermitting the adhesive attachment of the die to be readily be overcomesubsequent to testing and burnin.

Another alternate bonding technique uses water soluble hot melt glass.Water soluble hot melt glass is a thermoplastic material which melts atlow temperature. In the case of testing semiconductor die, thetemperature that the glass melts must be low enough to avoid damagingthe die. Subsequent to testing, the package body 13 is placed indeionized water, which causes the glass to dissolve, thereby freeing thedie 21. The package is then able to be reused.

Significantly, the leadwires 51 are not permanently bonded to thebondpads 27. Ohmic contact is established, but the bond is effected sothat the bonding force is less than that which would lift the bondpads27 from the die 21 when the wirebonds 51 are removed. This also enablesthe leadwires 51 to be lifted from the die 21 without destroying thebondpads 27. The leadwires 51 therefore are able to conduct signalsbetween the bondpads 27 and the contact pads 37.

Referring to FIG. 3, the bondpads 27 are a part of the die 21 and eitherthe entire bondpad 27 or possibly a part of the bondpad 27 may beseparated from the die 21 if sufficient force is applied to the bondpad27. This phenomena is known as "lifting" and is considered undesirable,because it results in destroying the die. For this reason, the leadwires51 are attached to the bondpads 27 with less bonding force retaining theleadwires 51 to the bondpads 27 than the attachment strength of thebondpads 27 to the die. In order to provide a margin for variation inthe fabricated bondpads 27, the strength of the bond between theleadwires 51 is significantly less than the attachment strength of thebondpads 27. This is preferably a ratio which ensures that the bondpads27 are not lifted from the die 21 when the leadwires 21 are removed bybreaking the bond between the leadwires 51 and the bondpads 27.

The relative wirebond:bondpad attachment strength should favor thebondpad even in cases where the wirebond is effected close to the edgeof the bondpad 27, as shown in FIG. 4. This should be 1:4wirebond:bondpad attachment strength, but lesser ratios, such as 1:2,1:1.5 or 1:1.3 would be effective.

In order to provide the reduced bonding force, a reduced size wirebondis used. This is particularly adaptable to the use of aluminum wirebond,in which ultrasonic vibration and pressure is used to attach thealuminum to the contact pads 37. The leadwire connection effected inthis manner is weakest at the location of attachment.

The wirebonder is a Kulicke & Soffa KS Model 1471 wirebonder, with whichaluminum wire is wedge bonded at ambient temperature. In conventionalwirebonding, a bond foot having a length of 2.5 mils is used with 1.25mil diameter aluminum wire. In the preferred embodiment, a wedge havinga bond foot of 0.5 mil (0.013 mm) in diameter was used. The wire size is0.7 mil (0.018 mm). This generates the following results:

                  TABLE 1                                                         ______________________________________                                        CONVENTIONAL INVENTIVE                                                        WEDGE BONDING TECHNIQUE                                                       ______________________________________                                        MATERIALS:                                                                    wedge          KS 60ABT-2025                                                                              KS 30ABT-1505                                     bond foot (length)                                                                           2.5 mils     0.5 mil                                           wire diameter  1.25 mils    0.7 mil                                           (1% SI/AL)                                                                    wire tensile   19-21 grams  13-15 grams                                       wire elongation                                                                              1-4%         0.5-2.0%                                          CHARACTERISTICS:                                                              actual bond size                                                                             2.25 × 3.0 mils                                                                      0.75 × 0.5 mils                             (width × length)                                                        MACHINE SETUP:                                                                wirefeed angle 60           30                                                bond type      forward      reverse                                           tearing motion tear         clamp                                             motor speed    90%          40%                                               init. bond force                                                                             32-38 grams  9-14 grams                                        MACHINE                                                                       PARAMETERS:                                                                   tip offset (mils)                                                                            10           15                                                velocity (mils/msec)                                                                         15           5                                                 time (msec)    15-25        20-40                                             power (mW)     90-105       18-28                                             force (grams)  5-8          2-8                                               loop height (mils)                                                                           12-18        6-9                                               clamp close    tear         bond                                              tail feed length (pulses)                                                                    45-60        12-17                                             tail tear length (pulses)                                                                    20-25        30-40                                             tail feed length (mils)                                                                      4.5-6.0      1.2-1.7                                           tail tear length (mils)                                                                      2.0-2.5      3.0-4.0                                           ______________________________________                                    

The result is a wirebond 71, shown in the photomicrograph of FIG. 4. Thewirebond, while being conductively effective, is easily removed from thedie 21 at completion of testing and burnin. The bond has similar bondproperties to conventional wirebonding on an intermolecular level, but,as a result of its smaller footprint, is easily removed. The removedwirebond, as shown in FIG. 5, leaves a damaged area 73 on the bondpad27. This is acceptable, and does not significantly deteriorate thebondpad 27 for later permanent wirebonding or other connection process.The larger scar 75 is a probe tip mark, resulting from probe pre-testingof the die 21 while still in wafer form.

As shown in FIGS. 4 and 5, the temporary wirebond 71 may be near theedge of the bondpad 27. The ratio of the strength of the bond betweenthe leadwires 51 to bondpad 27 to the attachment strength of thebondpads 27 must be sufficiently low to ensure that, even if thewirebond 71 is toward the edge of its bondpad 27, that bondpad 27 wouldnot be lifted from the die 21 when the leadwires 51 are removed.

As shown in FIGS. 1 and 2, the cover plate 15 is then placed on thepackage body 13. The cover plate 15 is preferably formed ofthermoplastic of thermosetting plastic, and is flanged (flanges 81-84).A pair of inwardly facing projections 87 extend from at least two of theflanges 81,82. The flanges 81-84 further serve to retard theintroduction of particles into the package body 13 during burnin andtest operations.

In the preferred embodiment, the wirebonder is used to remove theleadwires 51. The wirebonder is easily controlled to sweep across thewirebonds, and in the event that one of the wirebonders becomesinaccurate for its intended purpose, it is still likely to be usable tosweep wires which are attached by the inventive techniques. It is alsopossible to use a probe or tweezers to sweep the wires 51.

The connection is thereby removed without significantly damaging thedie. The die 21 itself is then removed, preferably with a tweezer-likeinstrument. If QL adhesive is used, thermal application is used in orderto facilitate removal of the die 21 from the package body 13.

Alternatively, chemical dissolution of the leadwires 51 can be used toremove the leadwires from the die 21. The chemical must be compatiblewith the die 21 while dissolving the leadwires 51.

After removal of the die 21, the leadwires 51 are removed from thepackage body 13. This may be accomplished mechanically, chemically or bymechanical sweep, followed by chemical removal. A preferred material forremoval of aluminum leadwires is sodium hydroxide (NaOH).

While specific locations for bondpads had not been specified, it ispossible to test a variety of configurations, including the conventionalarrangement of bondpads at the ends of the die 21. While a DIP packageis shown and described, it is possible to use surface mount and edgemount packages, such as quad flat packs (QFPs). The invention may alsobe used for testing die configured for LOC (leads over chip), as well asother designs. It is also possible to configure the package body 13 toinclude test circuitry in order to facilitate burnin or testing of thedie 21. In each of the above examples, the assembled fixture is adaptedinto conventional test equipment, such as a burn-in oven. What has beendescribed is a very specific configuration of a test fixture. Clearly,modification to the existing apparatus can be made within the scope ofthe invention. Accordingly, the invention should be read only as limitedby the claims.

We claim:
 1. Method for temporarily connecting a semiconductor circuitdie to external equipment for testing purposes in order to generatereliability and test data concerning the die, whereby the die may besubsequently disconnected, characterized by:a) placing the die in a diecarrier having a die receiving portion thereon, said die carrier havinga plurality of connectors thereon for connection to test circuitry, andsaid die carrier having a plurality of bondpads in close proximity ofthe die receiving portion; b) attaching leadwires to the die at bondpadson the die and attaching the leadwires to the bondpads on the diecarrier, said attachment of leadwires to the bondpads on the die beingwith sufficient bonding force to provide an electrical connection and toretain the leadwires on the bondpads on the die during a test sequence,and said bonding force being less than an attachment force of thebondpads on the die to the die and less than the tensile strength toseparate the leadwires from the bondpads; c) providing signals to atleast one of the bondpads on the die carrier in response to signals toat least one of the connectors, and providing signals to at least one ofthe connectors in response to signals which are present at least one ofthe bondpads; d) removing the leadwires from the bondpads on the die,resulting in the detachment of the leadwires to the bondpads on the die,wherein during said removal of the leadwires, bond attachment of theleadwires to the bondpads on the die is removed while the bondpadsremain intact on the die; and e) removing the die from the die carrier.2. Method as described in claim 1, further comprising:the step ofplacing the die in a die carrier including securing the die in the diecarrier with a material having a property of exhibiting a chargedsurface state sufficient and coefficient of friction sufficient to holdthe die in place without adhesive.
 3. Method as described in claim 1,further comprising:the step of placing the die in a die carrierincluding securing the die in the die carrier with a silicone stripwhich exhibits a charged surface state sufficient to hold the die inplace.
 4. Method as described in claim 1, further comprising:the step ofplacing the die in a die carrier including securing the die in the diecarrier by applying a liquid, and causing the liquid to be cured on thedie carrier, the cured liquid exhibiting a charged surface statesufficient to hold the die in place.
 5. Method as described in claim 1,further comprising:the step of placing the die in a die carrierincluding securing the die in the die carrier with a material whichexhibits a charged surface state sufficient to hold the die in placewithin the die carrier during the attachment of the leadwires to thebondpads on the die.
 6. Method as described in claim 5, furtherwherein:said material which exhibits a sufficient charged surface statebeing a silicone based polymer.
 7. Method as described in claim 5,further comprising:placing a lid over the die carrier after the die hasbeen placed in the die carrier, the lid providing a protective coverwhich prevents contaminants from entering the die cavity.
 8. Method asdescribed in claim 5, further comprising:a) placing a lid over the diecarrier after the die has been placed in the die carrier, the lidsecuring the die from movement; and b) the lid further providing aprotective cover which prevents contaminants from entering the diecavity.
 9. Method as described in claim 1, further comprising:a) placinga lid over the die carrier after the die has been placed in the diecarrier, the lid securing the die from movement; and b) the lid furtherincluding a material having a property of exhibiting a charged surfacestate, the charged surface state resulting in electrostatic attractionof free particles.
 10. Method as described in claim 9, furtherwherein:said material which exhibits a sufficient charged surface statebeing a silicone based polymer.
 11. Method as described in claim 9,further comprising:the step of placing the die in a die carrierincluding securing the die in the die carrier with a thermoplasticadhesive.
 12. Method as described in claim 1, further comprising:placinga lid over the die carrier after the die has been placed in the diecarrier, the lid securing the die from movement.
 13. Method as describedin claim 1, further comprising:said attachment of the leadwires to thedie being accomplished by laser bonding.
 14. Method as described inclaim 1, further comprising:said attachment of the leadwires to the diebeing accomplished by applying thermosonic energy applied through anthermosonic wirebonder.
 15. Method as described in claim 1, furthercomprising:said attachment of the leadwires to the die beingaccomplished by applying thermocompression energy applied through anthermocompression wirebonder.
 16. Method as described in claim 1,further comprising:said attachment of the leadwires to the die beingaccomplished by applying ultrasonic energy applied through an ultrasonicwirebonder.
 17. Method as described in claim 16, further comprising:saidattachment of the leadwires to the die being effected with a bondstrength which is less than one fourth the attachment strength of thebondpads to the die.
 18. Method as described in claim 16, furthercomprising:said attachment of the leadwires to the die being effectedwith a bond strength which is less than half the attachment strength ofthe bondpads to the die.
 19. Method as described in claim 16, furthercomprising:said attachment of the leadwires to the die being effectedwith a bond strength which is less than two thirds the attachmentstrength of the bondpads to the die.
 20. Method as described in claim16, further comprising:said attachment of the leadwires to the die beingat a bond strength selected such that said removal of the leadwiresresults in at least 50% of conventionally usable bondpad area remainingsubstantially undisturbed on the die.
 21. Method as described in claim1, further comprising:said detachment of the leadwires to the die beingaccomplished by chemical dissolution of the leadwires.
 22. Method asdescribed in claim 1, further comprising:removing the leadwires from thedie carrier, said detachment of the leadwires to the die beingaccomplished by chemical dissolution of the leadwires.
 23. Method asdescribed in claim 1, further comprising:said attachment of theleadwires to the die being accomplished by applying ultrasonic energyapplied through an ultrasonic wirebonder to conductive metallicleadwire, whereby, the wirebonder is selected to provide a bond sizewhich is less than 0.25× the bond size which is appropriate for apermanent wirebond for the die.
 24. Method as described in claim 1,further comprising:said attachment of the leadwires to the die beingaccomplished by applying ultrasonic energy applied through an ultrasonicwirebonder to aluminum leadwire, whereby, the wirebonder is selected toprovide a bond size which is less than 0.25× the bond size which isappropriate for a permanent wirebond for the die.
 25. Method asdescribed in claim 1, further comprising:said attachment of theleadwires to the die being accomplished by applying ultrasonic energyapplied through an ultrasonic wirebonder, whereby, the wirebonder isselected to provide a bond size which is less than 0.1× the bond sizewhich is appropriate for a permanent wirebond for the die.
 26. Method asdescribed in claim 1, further comprising:said detachment of theleadwires to the die being accomplished by applying a force of at least0.1 grams and no greater than 4.0 grams so that said removal of theleadwires leaves the bondpad suitable for ordinary ohmic contactattachment.
 27. Method as described in claim 1, further comprising:a)providing said die carrier with a hole in said die receiving portion;and b) applying force through said hole in order to assist said removalof the die from the die carrier.
 28. Method for connecting asemiconductor circuit die to external equipment for testing purposes andtesting the die, whereby the die may be subsequently disconnected,characterized by:a) providing a die carrier having a die receivingportion thereon, said die carrier having a plurality of connectorsthereon for connection to test circuitry, and said die carrier having aplurality of bondpads in close proximity of the die receiving portion;b) applying a water soluble glass to the die receiving portion; c)placing the die in the die receiving portion; d) permitting the watersoluble glass to bond to the die; e) attaching leadwires to the die atbondpads on the die and attaching the leadwires to the bondpads on thedie carrier, said attachment of leadwires to the bondpads on the diebeing with sufficient bonding force to provide an electrical connectionand to retain the leadwires on the bondpads on the die during a testsequence, and said bonding force being less than an attachment force ofthe bondpads on the die to the die and less than the tensile strength ofthe leadwires separate from the bondpads; f) providing signals to atleast one of the bondpads on the die carrier in response to signals toat least one of the connectors, and providing signals to at least one ofthe connectors in response to signals at least one of the bondpads; g)removing the leadwires from the bondpads on the die, resulting in thedetachment of the leadwires to the bondpads on the die, wherein duringsaid removal of the leadwires, bond attachment of the leadwires to thebondpads on the die is removed while the leadwires remain unsevered andthe bondpads remain intact; and h) dissolving the water soluble glasssufficiently to remove the die from the die carrier.
 29. Method asdescribed in claim 28, further comprising:a) the water soluble glassbeing water soluble hot melt glass, and further being a thermoplasticmaterial which melts at sufficiently low temperature to avoid damage tothe die; b) the dissolving of the water soluble glass being accomplishedby placing the die carrier in water, which causes the glass to dissolve,thereby freeing the die; and c) reusing the die carrier.